1. Field of the Invention
The present invention relates to a water heater in which the supply of hot water and temperature thereof are adjusted to a required level, and in which air staying in pipes, especially in a heat exchanger is discharged.
2. Description of the Related Art
There is a case where remaining air stays inside a water supply pipes etc. in a water heater. This remaining air may stay while concentrating in a certain place according to the arrangement of pipes in the water heater. There is also a case where warmer air stays in upper pipes in the water heater compared with cooler water according to a change in temperature of water or hot water in the pipes. Further, there is also a case where air stays in pipes when the water heater has not been used for a long time.
When remaining air stays inside a heat exchanger, heat is not exchanged sufficiently between exhaust and supplied water. Especially, when the flow rate of the supplied water to the inside of the heat exchanger is low, heating the water to setting temperature is difficult because air remaining thereinside cannot be pushed out.
It is known as a device that makes temperature of such supplied water flowing through the inside of a heat exchanger constant that means for bypassing a heat exchanger, flow rate adjustment means therefor are included and a bypass is closed after a start of operation to make water flow into the heat exchanger (for example, Japanese Laid-open Patent Publication No. 05-060337).
There is a problem that when remaining air stays inside a heat exchanger and heat is not exchanged sufficiently continuously, there may be a risk that temperature of a fin pipe of the heat exchanger becomes extraordinarily high to damage the heat exchanger.
There is a circulating instantaneous water heating system in which an air vent or an air separator, which is automatic air vent means, is disposed at upper pipes to remove the air. However, there is often a case that the system is not disposed because the system makes a device complex.
There is also a problem that: when a circulation pump in a water heater is started to operate, hot water in a heat exchanger is mixed with water in a bypass pipe; hot water of high temperature is not discharged even if a hot water faucet is opened just after the start of water heating; and remaining air cannot be discharged to stay in pipes.
Concerning such problems, there is no disclosure or suggestion thereof in Japanese Laid-open Patent Publication No. 05-060337, and no disclosure or suggestion about the structure etc. for solving them is presented.